High-pressure fuel pump for a fuel system of an internal combustion engine

Abstract

The invention relates to a high-pressure fuel pump. It is provided that this has a pump housing (12) and a delivery chamber (16) arranged in the pump housing (12), which is bounded by a piston (18) of the high-pressure fuel pump (10) which is displaceable in a longitudinal direction (28), wherein the high-pressure fuel pump (10) has an inlet valve (14) which opens from a low-pressure area (71) of the high-pressure fuel pump (10) towards the delivery chamber (16), and an outlet valve (20) which opens away from the delivery chamber (16) towards an outlet (34) of the high-pressure fuel pump (10), wherein the piston (18) is designed as a stepped piston with a region (18a) facing the delivery chamber (16) with a larger diameter and a region (18c) facing away from the delivery chamber (16) with a smaller diameter, wherein there is a gap between the region (18a) facing the delivery chamber (16) and the region (18c) facing away from the delivery chamber (16). a ring shoulder (18b) is formed on the opposite side (18c),wherein the area (18c) facing away from the conveying chamber (16) projects at least partially out of the pump housing (12), wherein a sleeve-shaped sealing carrier (64) is mounted on the pump housing (12) which secures a sleeve-shaped seal (62) in which the area (18c) facing away from the conveying chamber (16) is slidably sealed, wherein a sleeve-shaped stop element (66) is fixed in the sleeve-shaped sealing carrier (64) against which the annular shoulder (18b) comes into contact when the piston (18) is displaced maximally out of the conveying chamber (16). It is further provided that the piston (18) in its area (18a) facing the conveying chamber (16) has at least two circumferential grooves (19.1, 19.2) which lie at the axial height of the piston bushing (21) when the piston (18) is maximally displaced out of the conveying chamber (16) and also when the piston (18) is maximally displaced into the conveying chamber (16).

Description

State of the art

[0001] From DE 10 2020 215 458 A1 A1 of the applicant, a high-pressure fuel pump is already known which has a piston oscillating in a piston bushing. Disclosure of the invention

[0002] The invention is based on the desire of the inventors to occasionally operate fuel high-pressure pumps according to the preamble of claim 1 for a longer period of time at high speed, but without pressure and without pumping fuel.

[0003] Investigations have shown that the resulting friction and the lack of fuel delivery can lead to excessive local heating in the area of ​​the piston and piston liner, particularly if misalignments occur between the piston and the piston liner.

[0004] The resulting thermal expansion can consume any clearance provided between the piston and the piston bushing, creating the risk of seizure of the piston and piston bushing and failure of the high-pressure fuel pump.

[0005] In order to always avoid such excessive heating, it is provided according to the invention that the piston has at least two circumferentially extending grooves in its region facing the delivery chamber, which grooves are located at the axial height of the piston bushing when the piston is maximally displaced out of the delivery chamber and also when the piston is maximally displaced into the delivery chamber.

[0006] The at least two piston grooves can, for example, be exactly two piston grooves or more than two. The piston grooves can, for example, be at least 0.3 mm deep in the radial direction. The piston grooves can, for example, be at least 0.5 mm wide in the axial direction. The piston grooves can, for example, have a rectangular, round, triangular, or polygonal cross-sectional area.

[0007] The at least two circumferential grooves intensify the exchange of fuel in the gap between the piston and the piston sleeve. By removing already heated fuel and supplying fresh, cool fuel, the piston and the piston sleeve are reliably cooled, and excessive, especially local, heating is reliably prevented. As a result, the pump according to the invention reliably prevents seizure and pump failures.

[0008] If the piston bushing has a second axial end that points away from the delivery chamber, and the part of the piston facing the delivery chamber slides over this second axial end of the piston bushing during operation of the high-pressure fuel pump, increased friction can occur locally at this position and thus heat can be generated, especially if there is an inclination between the piston and the piston bushing.

[0009] In order to reliably avoid excessive local heating of the piston or piston bushing in this situation as well, a further development of the invention provides that the at least two circumferentially extending grooves comprise a first groove and a second groove, wherein the first groove is arranged in the axial direction on the side of the second groove facing the delivery chamber, wherein the piston bushing has a first axial end facing the delivery chamber and a second axial end facing away from the delivery chamber, wherein the second groove is spaced apart in the axial direction by a distance from the second axial end of the piston bushing when the piston is maximally displaced out of the delivery chamber, wherein the distance is 10 µm to 2 mm.

[0010] During operation of the high-pressure fuel pump, the second groove then comes into the immediate vicinity of the second axial end of the piston bushing and, precisely where local heating potentially occurs, causes an exchange of the fuel located in the gap between the piston and the piston bushing and thus a local cooling.

[0011] A further development of the invention can provide that the distance is between 25 µm and 1 mm, or 25 µm to 500 µm, in particular 50 µm.

[0012] If an inner edge of the piston bushing is chamfered in the area of ​​the second axial end of the piston bushing, it can be provided that the distance dimension is only measured on the extension facing the conveying chamber as seen from the chamfer, so that the axial extension of the chamfer is not taken into account for determining the distance dimension.

[0013] The high-pressure fuel pump according to the invention can be used in particular in so-called PDI systems. These are systems for supplying fuel to an internal combustion engine that provide both the temporary direct injection of fuel at high pressure (e.g., >100 bar) into the combustion chambers of the internal combustion engine and the temporary injection of fuel into the intake chamber of the internal combustion engine at low pressure (e.g., <10 bar).

[0014] The high-pressure fuel pump according to the invention serves to compress the fuel under high pressure. During phases in which compressed fuel is not required, the high-pressure fuel pump according to the invention can easily run for extended periods at high speed, but without pressure and without delivering fuel, without causing problematic local heating in the area between the piston and the piston sleeve.

[0015] Exemplary embodiments of the invention are explained below with reference to the drawing. In the drawing: Fig. 1 a high-pressure fuel pump according to an exemplary embodiment, the pump piston of which is located at a top dead center; Fig. 2 a partial view of the high-pressure fuel pump from the Fig. 1, whose pump piston is pulled out of the pump housing and the pumping chamber to its maximum extent (“delivery condition”).

[0016] In Fig. 1, a high-pressure fuel pump for an internal combustion engine (not shown in detail) bears the reference numeral 10. The high-pressure fuel pump 10 has a substantially cylindrical pump housing 12, in or on which the essential components of the high-pressure fuel pump 10 are arranged. Thus, the high-pressure fuel pump 10 has an inlet / quantity control valve 14, a piston 18 delimiting the delivery chamber 16 and capable of reciprocating motion by a drive shaft (not shown), an outlet valve 20, and a pressure relief valve 22.

[0017] In the housing 12, there is a first channel 24 which extends coaxially to the delivery chamber 16 and the piston 18 and which leads from the delivery chamber 16 to a second channel 26 formed by a recess, which is arranged at an angle of 90° to the first channel 24 and in which the pressure relief valve 22 is accommodated. The pump housing 12 has a longitudinal axis 28 along which the piston 18 is displaceable. Fig. 1 above, a pressure damper 30 is arranged in the pump housing 12 between the pump cover 12b on the one hand and the pump body 12a on the other hand.

[0018] During operation, fuel is sucked into the delivery chamber 16 by the piston 18 during a suction stroke via the inlet and quantity control valve 14. During a delivery stroke, the fuel in the delivery chamber 16 is compressed and expelled via the outlet valve 20, for example into a high-pressure region 32, for example to a fuel rail, where the fuel is stored under high pressure. The high-pressure region 32 is connected to the high-pressure fuel pump 10 via an outlet connection 34. The amount of fuel expelled during a delivery stroke is adjusted by the electromagnetically actuated inlet and quantity control valve 14. If there is an impermissible overpressure in the high-pressure region 32, the pressure relief valve 22 opens, allowing fuel to flow from the high-pressure region 32 into the delivery chamber 16.

[0019] It is further provided that the piston 18 is designed as a stepped piston, with a region 18a facing the delivery chamber 16 with a larger diameter and a region 18c facing away from the delivery chamber 16 with a smaller diameter, wherein an annular shoulder 18b is formed between the region 18a facing the delivery chamber 16 and the region 18c facing away from the delivery chamber 16, wherein the region 18c facing away from the delivery chamber 16 protrudes at least partially from the pump housing 12, wherein a sleeve-shaped seal carrier 64 is mounted on the pump housing 12, which fixes a sleeve-shaped seal 62, in which the region 18c facing away from the delivery chamber 16 is sealingly displaceable, wherein a sleeve-shaped stop part 66 is fixed in the sleeve-shaped seal carrier 64, against which the annular shoulder 18b comes to rest when the piston 18 is maximally out of the delivery chamber 16 is shifted out (as in the Fig. 2 is maximally displaced downward), which can be the case, for example, when handling the high-pressure fuel pump 10 prior to installation in an internal combustion engine ("as-delivered condition"). In this situation, the stop member 66 prevents the piston 18 from falling out of the pump housing 12.

[0020] The piston spring 75 is also supported in a circumferential groove 64a of the seal carrier 64. The piston spring 75 further acts on the piston 18 via a spring plate 77 fixed to the piston 18 in the direction away from the delivery chamber 16 (in the Fig. 1 down).

[0021] Between the seal carrier 64 and the pump body 12a, a fluid chamber 79, also referred to as a step chamber or compensation chamber, is formed, which is connected via a longitudinal bore in the pump body 12a (not shown in the figures) to the chamber arranged between the pump cover 12b and the pump body 12a, and in which the pressure damper 30 is arranged.

[0022] The piston 18, with its region 18a facing the delivery chamber 16, is displaceable in the axial direction 28 in a piston bushing 21 fixed in the pump housing 12. The piston bushing 21 has a first axial end 21.1 facing the delivery chamber 16 and a second axial end 21.2 facing away from the delivery chamber 16. In the example, the outer surface of the region 18a of the piston 18 facing the delivery chamber 16 always projects beyond the piston bushing 21 in both axial directions.

[0023] In the example, the piston 18 has exactly two circumferential grooves 19.1, 19.2 in its region 18a facing the delivery chamber 16. This is a first groove 19.1, which is arranged in the axial direction on the side of the second groove 19.2 facing the delivery chamber 16.

[0024] In the example, it is provided that the second groove 19.2 is spaced apart in the axial direction by a distance dimension d from the second axial end 21.2 of the piston bush 21 when the piston 18 is maximally displaced out of the delivery chamber 16, as shown in the Fig. 2 is the case. The distance d in this example is 0.05 mm.

[0025] Alternatively, one or more additional grooves may be provided in the region 18a of the piston 18 facing the delivery chamber 16, for example, between the first groove 19.1 and the second groove 19.2. Fuel transport in the sealing gap between the piston 18 and the piston bushing 21 can thus be further improved.

[0026] The additional groove(s) can, for example, be 0.5mm deep and wide or less. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2020 215 458 A1

[0001]

Claims

[1] A high-pressure fuel pump (10) for a fuel system of an internal combustion engine, comprising a pump housing (12) and a delivery chamber (16) arranged in the pump housing (12), which is delimited by a piston (18) of the high-pressure fuel pump (10) and which is displaceable in an axial direction (28) in a piston bushing (21) fixed in the pump housing (12), wherein the high-pressure fuel pump (10) has an inlet valve (14) which opens from a low-pressure region (71) of the high-pressure fuel pump (10) to the delivery chamber (16), and an outlet valve (20) which opens away from the delivery chamber (16) towards an outlet (34) of the high-pressure fuel pump (10), wherein the piston (18) is designed as a stepped piston, with a region (18a) facing the delivery chamber (16) and having a larger diameter and a region (18b) extending from the delivery chamber (16) opposite area (18c) with smaller diameter,wherein an annular shoulder (18b) is formed between the region (18a) facing the delivery chamber (16) and the region (18c) facing away from the delivery chamber (16), wherein the region (18c) facing away from the delivery chamber (16) protrudes at least partially from the pump housing (12), wherein a sleeve-shaped seal carrier (64) is mounted on the pump housing (12), which fixes a sleeve-shaped seal (62) in which the region (18c) facing away from the delivery chamber (16) is sealingly displaceable, wherein a sleeve-shaped stop part (66) is fixed in the sleeve-shaped seal carrier (64), against which the annular shoulder (18b) comes to rest when the piston (18) is maximally displaced out of the delivery chamber (16), , characterized bythat the piston (18) has, in its region (18a) facing the delivery chamber (16), at least two circumferentially extending grooves (19.1, 19.2) which, when the piston (18) is maximally displaced out of the delivery chamber (16), and also when the piston (18) is maximally displaced into the delivery chamber (16), lie at the axial height of the piston bush (21). [2] High-pressure fuel pump (10) according to claim 1, wherein the at least two circumferentially encircling grooves (19.1, 19.2) comprise a first groove (19.1) and a second groove (19.2), wherein the first groove (19.1) is arranged in the axial direction on the side of the second groove (19.2) facing the delivery chamber (16), wherein the piston bush (21) has a first axial end (21.1) facing the delivery chamber (16) and a second axial end (21.2) facing away from the delivery chamber (16), wherein the second groove (19.2) is spaced apart in the axial direction by a distance dimension (d) from the second axial end (21.2) of the piston bush (21) when the piston (18) is maximally displaced out of the delivery chamber (16), wherein the distance dimension (d) is 10 µm to is 2mm. [3] High-pressure fuel pump (10) according to claim 1, wherein the distance dimension (d) is 25 µm to 1 mm, in particular 50 µm. [4] High-pressure fuel pump (10) according to one of the preceding claims, wherein the at least two piston grooves (19.1, 19.2) are at least 0.3 mm deep in the radial direction. [5] High-pressure fuel pump (10) according to one of the preceding claims, wherein the at least two piston grooves (19.1, 19.2) are at least 0.5 mm wide in the axial direction. [6] High-pressure fuel pump (10) according to one of the preceding claims, wherein the at least two piston grooves (19.1, 19.2) have a rectangular, round, triangular or polygonal cross-sectional area.

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